Yes and no, you couldnt just screw the aerial to the lightbar madhatman is right, you could take the magmount apart and make something to fit, however your better off either using a 'snailmount' which would bolt to the spare lug, or better a truckers mirror mount, one of these just clamps around your bars and away you go, you do need to make sure that there is a good connection from the bracket to the bar otherwise your SWR will be high and your range will be crap, a piece of thick wire from the bracket through the grille to a good body earth is reccomended.
Oh and make sure the whip cannot flex and touch the body or bull bars, if you were transmitting and this happened you'd blow something.